Composite live hinge

ABSTRACT

A hinged component includes first and second portions of material coupled together by a composite live hinge. The live hinge includes a layer of tensile fabric and a layer of elastomer interposed between the tensile fabric and the material of one or both of the coupled first and second portions. The composite live hinge is capable of joining structural composite materials without the need for scoring, and thereby weakening, the structural composite material along the desired hinge line. The live hinge can be embedded in the materials it joins in a method that is compatible with traditional structural composite layup processes and in a manner which prevents resin from the structural composite materials from infiltrating the tensile fabric and compromising its flexibility.

TECHNICAL FIELD

This application relates generally to live hinge structures that providehinged movement between components via material flexure.

BACKGROUND

Conventional hinges are used to attach two or more components togetherso that the components are moveable relative to each other with onerotational degree of freedom and typically about a pivot axis. Somehinges include dedicated components that move relative to each other,such as a pin and barrel, where the pin defines the pivot axis and aninner cylindrical surface of the barrel rides along an outer surface ofthe pin. Another type of hinge is a live hinge or living hinge. Atypical living hinge is formed at a joint between two portions of thesame piece of material and is thus made from the same material as thetwo portions of material it joins. This type of live hinge allows hingedmovement between the portions of the piece of material on opposite sidesof the hinge by flexure or bending of the material along a hinge line.Living hinges function without the friction and wear associated withother types of hinges. The location of a living hinge joint is oftendetermined by a thinned or otherwise weakened area in the monolithiccomponent.

SUMMARY

In accordance with one embodiment, a hinged component includes a firstportion of material, a second portion of material, and a live hingeattaching the first and second portions of material together at a hingeregion. The live hinge includes a layer of tensile fabric and a layer ofelastomer interposed between the tensile fabric and the material of atleast one of the first and second portions where the live hinge isattached to each of the first and second portions.

In accordance with another embodiment, a method of making a hingedcomponent includes the steps of: (a) overlapping a layer of tensilefabric with a layer of elastomer; (b) locating the overlapped layers ina component forming tool; (c) introducing polymer-based material intothe forming tool, so that a first portion of polymer-based materialoverlaps one end of the layered materials and a second portion ofpolymer-based material overlaps an opposite end of the layeredmaterials; and (d) forming the portions of polymer-based material to adesired shape using the forming tool so that the layers of tensilefabric and elastomer form a live hinge between the first and secondportions of polymer-based material.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages will become apparent to thoseskilled in the art in connection with the following detailed descriptionand drawings of one or more embodiments, in which:

FIG. 1 is an isometric view of an embodiment of a hinged componentincluding a live hinge;

FIG. 2 is a perspective view of a tail portion of an air vehicle,including an embodiment of the hinged component;

FIG. 3 is a cross-sectional view of the hinged component taken alongline 3-3 of FIG. 1;

FIG. 4 is an enlarged view of a portion of the hinged component of FIG.3, showing one end of the live hinge embedded in a portion of material;

FIG. 5 is an enlarged view of a hinge region of the hinged component ofFIG. 3;

FIG. 6 is an isometric view of an illustrative forming tool for thecomposite live hinge; and

FIG. 7 is a process flow chart summarizing one embodiment of a method ofmaking the hinged component with the composite live hinge.

DETAILED DESCRIPTION

An enhanced composite live hinge is described below and represents adifferent approach for live hinge configurations. In this approach, thelive hinge is not necessarily formed from the same material(s) as theportions of material it joins. The composite live hinge includes morethan one layer of material, making it possible to tailor each layer toperform a specific function and/or address a certain problem withconventional hinge configurations. This approach may be particularlyadvantageous in applications in which the materials joined by the hingeare too stiff for the live hinge to be formed in a monolithic componentwithout additional material weakening at the desired hinge jointlocation, such as with structural composites. Some embodiments of thelive hinge described herein can also provide nearly unlimited fatiguelife with a full 360° angular range of movement. Other advantages willbecome apparent to skilled artisans.

An illustrative hinged component 10 is illustrated in FIG. 1 andincludes a first portion of material 12, a second portion of material14, and a live hinge 16 attaching the first and second portions ofmaterial together at a hinge region 18. As used herein, a hinge is anelement that pivotally couples at least two components or portions ofmaterial together with one rotational degree of freedom. A live hinge isa hinge that provides the rotational degree of freedom via flexure orbending rather than relative pivotal motion between pivotablyinterconnected hinge elements. The live hinge 16 couples the first andsecond portions 12, 14 together for hinged movement generally about apivot axis A, though the live hinge does not necessarily define thepivot axis in the same sense as pin and barrel style hinges, forexample. The first portion 12 is shown in dashed lines in a position itwould be in after having undergone hinged movement relative to thesecond portion 14 in direction B. In the illustrated example, thecoupled portions of material 12, 14 are flat portions of material butcould be any shape, depending on the application. In one embodiment, thehinged component 10 is an air vehicle component. For example, FIG. 2illustrates a tail portion of an air vehicle 100. Here, the verticalstabilizer of an air vehicle includes the hinged component 10 with astabilizer body 12 of the vertical stabilizer comprising the firstportion of the hinged component 10 and a rudder 14 of the verticalstabilizer comprising the second portion of the hinged component 10. Therudder 14 is coupled to the body 12 by live hinge 16 at hinge region 18.

Live hinges are useful in applications such as Radio Control (RC)aircraft and Unmanned Air Vehicles (UAVs), for example, wherelightweight structural composites are widely used, and where it isuseful to reduce the weight and complexity of moving parts. Other airvehicle components, such as elevators, trim tabs, wings flaps, ailerons,spoilers, slats, etc., may also employ live hinges. These are only a fewexamples of suitable applications for the composite live hinge describedherein, as they may be suitable for use in non-moving air vehiclecomponents and/or non-air vehicle components.

FIGS. 3-5 are cross-sectional views showing portions of the hingedcomponent of FIG. 1. FIG. 3 shows opposite ends 20, 22 of the hinge in asingle view, FIG. 4 is an enlarged view of one of the ends 20, and FIG.5 is an enlarged view of a central portion 24 of the hinge. Withreference to FIGS. 3-5 as necessary, one end 20 of the hinge 16 isattached to the first portion of material 12, and the opposite end 22 isattached to the second portion of material 14. One or both of the hingeends 20, 22 may be at least partially embedded in the material of therespective first and second portions 12, 14. In this case, both ends 20,22 are embedded in the respective portions of material, and the centralportion 24 of the hinge is exposed (i.e., not covered or concealed bythe materials of the joined portions 12, 14). Both of opposite sides 26,28 of the hinge 16 may be exposed as shown, or only one side may beexposed. It is also possible to construct the hinged component 10 sothat none of the hinge 16 is exposed. Techniques for embedding portionsof the hinge 16 in the joined portions 12, 14 are described in furtherdetail below, and this is only one manner of attaching the hinge 16 toportions 12, 14. For example, the hinge 16 could have one or both of itsopposite ends 20, 22 bonded, embedded or otherwise attached directly toone side of each of portions 12, 14.

The illustrated hinge 16 includes a layer of tensile fabric 30 and alayer of elastomer 32 interposed between the tensile fabric and thematerials of the first and second portions 12, 14 at locations where thelive hinge 16 is attached to each of the portions of material. This isbest shown in FIG. 4, where one end 20 of the hinge 16 is embedded inthe material of first portion 12. In this particular example, thetensile fabric 30 is interposed between two layers of elastomer 32, andeach layer of elastomer is interposed between the tensile fabric and thematerials of the first and second portions at the hinge attachmentlocations. Stated differently, hinge 16 includes the layer of tensilefabric 30 interposed or sandwiched between two layers of elastomer 32,and portions of the hinge 16—in this case, opposite ends 20, 22—areinterposed between layers of the first and second material portions 12,14. The layer(s) of elastomers 32 may extend between the opposite ends20, 22 of the hinge and/or be coextensive with the layer of tensilefabric 30, as shown, or the elastomers may be present only where thehinge 16 is attached to the corresponding material portion 12, 14.

The layered structure of the composite hinge 16 enables customization ofhinge properties and characteristics not possible with live hingesformed from a single piece of material. For example, the layer oftensile fabric 30 may be selected to optimize or maximize the strengthof the composite hinge 16, without regard for whether the selectedmaterial for layer 30 is compatible with the portions of material 12, 14it helps join in hinged fashion. Likewise, the layer(s) of elastomer 32may be selected to optimize or maximize flexibility of the hinge 16,without regard for its strength or ability to hold the two portions 12,14 together on its own. Examples of suitable materials for the layer oftensile fabric 30 and the elastomer 32 are given below.

The layer of tensile fabric 30 may be a layer of material with majordimensions in two Cartesian directions (i.e., in a plane) and arelatively small thickness in the third Cartesian dimension. Thestrength properties of the tensile fabric 30 may be significant only inthe planar directions, which is to say that tensile properties of thetensile fabric may not be practically measurable for a given sample inany out-of-plane direction. Suitable types of materials for the layer oftensile fabric 30 are virtually unlimited and may include polymeric ormetallic materials, natural or synthetic materials, woven or non-wovenmaterials, and layered or non-layered materials, for example. In oneembodiment, the layer of tensile fabric 30 includes or is a meshmaterial. A mesh material is generally a material made up of strands ofsolid material arranged in one or more directions in the plane of thelayer with open spaces between at least some of the individual strands.Some examples include woven or knitted material, screening or netting.The solid portion of the mesh material may be polymeric, metallic,glass, carbon fibers, or any other material or combination of materials.Some examples of polymeric materials suitable for use as the meshmaterial include polyamides (i.e., nylon) or polyesters. One suitablemesh material is RVB mesh, available from Airtech Europe Sarl(Luxembourg). One advantage of mesh materials is that material from theillustrated elastomer layers 32 can extend through the open portions ofthe mesh to interconnect or fuse together during formation of the livehinge, consistent with the exemplary methods described in more detailbelow. The thickness of the layer of tensile fabric 30 may be in a rangefrom about 0.1 to about 0.5 mm. In one specific example, the thicknessof the layer 30 is about 0.3 mm. The layer of tensile fabric 30 mayitself be formed from multiple layers or sublayers of material. Forexample, the tensile fabric 30 may include a plurality of unidirectionallayers of fibers, such as glass fibers, with each layer having thefibers oriented in different directions within the plane of the layer.

The layer or layers of elastomer 32 may be formed from any type ofelastomer, such as natural rubber or any synthetic elastomer (e.g., athermoplastic elastomer or a curable or thermoset elastomer). Theelastomer may be selected and used to help protect the layer of tensilefabric 30 during processing and/or during hinge use. For example, thelayer of elastomer 32 can help prevent components of the material fromportions 12, 14 of the hinged component from infusing into orimpregnating the layer of tensile fabric 30. In addition, the layer ofelastomer can help protect the layer of tensile fabric from exposure tothe environment (e.g. UV exposure, moisture, etc.) during hinge service.The elastomer may also provide an intermediate material that can bondwith both the layer of tensile fabric 30 and the material of the firstand second portions, thus facilitating attachment of the hinge 16 toportions 12, 14. Examples of suitable materials for use in the layer ofelastomer material 32 include fluoroelastomer compounds available fromEagle Elastomer, Inc. (Cuyahoga Falls, Ohio). Fluoroelastomers mayprovide certain benefits, such as high-fatigue life, resistance toweathering, and resilience to adhesion with other materials. Forexample, fluoroelastomers may offer certain processing advantagesbecause, where the central portion 24 of the hinge is exposed, theexposed portion remains free of unwanted constituents that may stiffenthe hinge or otherwise affect its flexibility. Silicone elastomers mayprovide similar benefits. When combined with the layer of tensile fabric30, the importance of the tensile strength or tear strength of theelastomer layer becomes less significant, as those hinge properties canbe provided by the tensile fabric. Each layer of elastomer may itselfinclude multiple layers or sublayers of elastomer.

Consistent with the description of the methods below, anotherconsideration for the layer of elastomer 32 is its ability to bond withthe material of the first and second portions 12, 14 of the hingedcomponent. For example, the elastomer may be selected so thatcross-links are formed between the layer of elastomer and the materialof portions 12, 14. Where multiple layers of elastomer are used, asshown in the figures, each layer may have the same or differentcomposition. The thickness of each layer of elastomer material 32 may bein a range from about 0.1 to about 0.5 mm. In one specific example, thethickness of the layer(s) 32 is about 0.3 mm. Each of the individuallyillustrated layers of elastomer 32 may itself be formed from multiplelayers or sublayers of elastomer, as well.

Each of the first and second portions 12, 14 of the hinged component mayinclude a polymeric constituent. For example, each of portions 12, 14may be a reinforced polymer composite with reinforcing fibers orparticles distributed in a polymeric matrix. One example of a reinforcedpolymer composite is an injection molding grade of glass-filledpolyamide material. Another example of a reinforced polymer composite isa structural composite including a thermoset polymer matrix, such asepoxy, polyester, or acrylic matrix. The reinforcing fibers may beglass, organic (e.g. polyaromatic), carbon, metallic, or any othersuitable material. Some examples of structural composite materials thatcould serve as first and/or second portions 12, 14 are primarilycomposed of the reinforcing material. For example, glass or Kevlarfibers or mats of fibers may be impregnated with a curable resin to formstructural composite portions 12, 14. In one embodiment, the reinforcingfibers of the first and second portions of material 12, 14 and the layerof tensile fabric 20 are the same material (e.g., Kevlar fibers), withthe fibers of the first and second portions being impregnated with apolymer resin and the fibers of the tensile fabric being substantiallyfree of the polymer resin of portions 12, 14. In another embodiment, thereinforcing fibers of the first and second portions 12, 14 and thetensile fabric are different material types. As used in this context, adifferent material type is a material that is different in compositionand/or form from another material. For example, a polyester tensilefabric and Kevlar reinforcing fibers are different material typesbecause of the different material composition, even if both are in wovenform. Likewise, chopped glass reinforcing fibers and woven glass fibertensile fabric are different material types because of their differentform, even though both have a glass composition. Also, differentmaterial compositions of the same material family constitute differentmaterial types, such as nylon 6 compared to nylon 6,6 or two differentglass chemistries. The first and second portions could also be formedfrom unreinforced polymeric materials. Polymeric materials with reactivegroups that can form cross-links with the layer(s) of elastomer material32 may be preferred. First and second portions 12, 14 with polymericcomponents may facilitate encapsulating or embedding of desired portionsof the composite hinge 16 as shown in the figures. But the compositehinge 16 described herein could be used to form a hinge joint betweenother types of material portions.

In the illustrated example, each of the first and second portions ofmaterial 12, 14 includes multiple layers of material, with the layersbeing separated where they overlap with the hinge, but adjacent oneanother as a single layer of thicker material outside the hinge region,as is best shown in FIG. 4. Stated differently, in the embodiment shownin the figures, the ends 20, 22 of the hinge 16 are interposed betweenlayers of material portions 12, 14. Thus, the hinged component 10 isthicker where the hinge 16 is attached to the first and second portions12, 14 than it is at locations away from the hinge attachment locations.In configurations where the central portion 24 of the hinge 16 isexposed, the hinged component 10 is also thinner at the central portionof the hinge than at the opposite ends 20, 22 of the hinge. In suchembodiments, the hinge 16 thus forms a portion of the opposite surfacesof the hinged component 10 where it interconnects the first and secondportions of material 12, 14.

Reference is made to FIGS. 6 and 7 to describe an illustrative method ofmaking the hinged component. FIG. 6 illustrates an exemplary formingtool 200 for the above-described hinged component, and FIG. 7 is aprocess flow chart summarizing the illustrative method. The method mayinclude the following steps: overlapping a layer of tensile fabric 230with a layer of elastomer 232, locating the layers 230, 232 in thecomponent forming tool 200, introducing polymer-based material into theforming tool 200, and forming the portions of polymer-based material212, 214 to a desired shape. The step of introducing polymer-basedmaterial into the forming tool 200 is performed so that a first portionof polymer-based material 212 overlaps one end 220 of the layeredmaterials and a second portion of polymer-based material 214 overlaps anopposite end 222 of the layered materials, and the step of forming isperformed so that the layers of tensile fabric 230 and elastomer 232form the live hinge 16 between the first and second portions ofpolymer-based material, which correspond to the first and secondportions 12, 14 of the finished hinged component 10.

In the example of FIG. 6, the polymer-based material that is introducedto the forming tool is in the form of curable sheets of pre-pregmaterial, consistent with a layup process for structural panels. In thisparticular example, multiple sheets of pre-preg material are providedfor each of the first and second portions, with two layers of pre-pregoverlapping the underside of the layered hinge components 230, 232 andtwo layers overlapping the topside of the layered components 230, 232.Pre-preg material includes reinforcing fibers impregnated with athermosetting resin that is only partially cured—i.e., sufficientlycured for purposes of handling, but sufficiently uncured to allow theresin to be shaped under heat and/or pressure. Here, also, multiplelayers of elastomer 232 are provided. Various arrangements of materiallayers may be used, including multiple layers of tensile fabric 230 withor without interposed layers of elastomer, etc.

In the illustrated example, the method also includes the step of curingthe pre-preg material while it is in the desired shape of the hingedcomponent. Surfaces of the forming tool 200 are configured to providethe desired shape. This process illustrates additional criteria that maybe used when selecting hinge materials, in that the tensile fabric andthe elastomer of the hinge must be capable of withstanding the formingconditions (temperature, pressure, etc.) when embedded or overmolded asdescribed here. For example, either one or both of the tensile fabric230 or the elastomer 232 may be provided as curable materials so thatone or both are co-cured with the pre-preg sheets of material. In oneexample, the elastomer 232 is provided as a curable material and, underthe heat and pressure of the forming step, flows at least partiallythrough the tensile fabric and co-cures with the pre-preg material, thusforming an elastomer-infused tensile fabric layer at the core of thecomposite hinge 16. In another example, the elastomer 232 is provided inthe form of a material with reactive groups that react with the polymerportion of the pre-preg material to form cross-links (i.e., covalentchemical bonds) between the elastomer and the material of the first andsecond portions of material where the materials overlap in the formingtool.

The method can also be performed so that the hinged component includesthermoplastic materials as the first and second portions. For example,the step of introducing polymer-based material to into the forming tool200 may include injecting a reinforced or unreinforced moltenthermoplastic resin into a mold cavity of the tool in an overmoldingoperation. In this embodiment, the tool surfaces are cooled instead ofheated to solidify the molten resin. In either case, the layer or layersof elastomer 232 can be arranged in the forming tool to substantiallyprevent the polymer-based material from infiltrating the tensile fabric230. This allows the layer of tensile fabric to maintain its fabric-likecharacter in the finished hinged component, whereas, without theelastomer layer or layers helping to prevent polymer infiltration, thetensile fabric could become impregnated with polymer resin from thefirst and second portions of material which, when hardened or cured,would make rigidify the tensile layer to the stiffness of the joinedfirst and second portions. Where resin from the first and secondportions 12, 14 (or 212 and 214 in FIG. 6) infiltrates the fibers of thetensile layer of the hinge—such as in the absence of the protectivelayers of elastomer—the finished component would require further scoringor other weakening along the desired hinge line in order to allow thehinge to bend. This type of additional weakening along the hinge line isundesirable, as it can damage the fibers of the tensile layer.

This is one of the problems presented when attempting to form atraditional live hinge from a single piece of structural compositematerial. Such materials are simply too stiff and strong to form a livehinge without breaking at least some of the reinforcing fibers and thusnecessarily weakening the material at the hinge joint. Where scoring isused in such examples, the flexibility of the hinge joint is somewhatdependent on which side of the material is scored, cut, or otherwiseweakened—i.e., the resulting hinge joint may be more flexible in onedirection of pivoting than in the other direction. The composite livehinge described above can be made without scoring any portion of thehinged component along the desired hinge region so that the materialsused to form the hinge maintain their full strength with no unnecessarystress concentrators along the finished component.

The resulting composite hinge 16 also provides design redundancy. Forexample, even in the elastomer layer is in some way damaged or reaches apoint of fatigue, the tensile fabric continues to hold the first andsecond portions of the hinged component together. Mechanical testing ofexperimental samples of the above described composite hinge indicatesthat, after a 100,000 use cycle, the hinge is fully functional, even ifthe outermost layers of elastomer are completely failed. Moreover, thecomposite hinge has a liner life cycle that is not negatively impactedover time, unlike traditional live hinges formed in composite materials,which are continually progressing toward laminate failure and require aninitial break-in period.

It is to be understood that the foregoing is a description of one ormore illustrative embodiments of the invention. The invention is notlimited to the particular embodiment(s) disclosed herein, but rather isdefined solely by the claims below. Furthermore, the statementscontained in the foregoing description relate to particular embodimentsand are not to be construed as limitations on the scope of the inventionor on the definition of terms used in the claims, except where a term orphrase is expressly defined above. Various other embodiments and variouschanges and modifications to the disclosed embodiment(s) will becomeapparent to those skilled in the art. All such other embodiments,changes, and modifications are intended to come within the scope of theappended claims.

As used in this specification and claims, the terms “for example,” “forinstance,” “such as,” and “like,” and the verbs “comprising,” “having,”“including,” and their other verb forms, when used in conjunction with alisting of one or more components or other items, are each to beconstrued as open-ended, meaning that the listing is not to beconsidered as excluding other, additional components or items. Otherterms are to be construed using their broadest reasonable meaning unlessthey are used in a context that requires a different interpretation.

What is claimed is:
 1. A hinged component, comprising: a first portionof material; a second portion of material; a first layer of elastomer; alive hinge attaching the first and second portions of material togetherat a hinge region, the live hinge comprising a layer of tensile fabricat least partially infiltrated by at least part of the first layer ofelastomer; at least part of the first layer of elastomer beinginterposed between the tensile fabric and material of the first andsecond portions; at least one of the portions of material including astructural composite comprising reinforcing fibers in a polymer matrix;and the first layer of elastomer being co-cured with at least one of theportions of material.
 2. The hinged component of claim 1, wherein thefirst layer of elastomer and at least one of the first and/or secondportions of material are cross-linked together by covalent bonds.
 3. Thecomponent of claim 1, wherein the reinforcing fibers and the tensilefabric are different material types.
 4. The component of claim 1,wherein the first layer of elastomer and at least one of the first andsecond portions of material are cross-linked together where the livehinge is attached to each of the first and second portions.
 5. Thecomponent of claim 1, wherein the tensile fabric is a polymeric meshmaterial.
 6. The component of claim 1, wherein the first layer ofelastomer comprises a fluoroelastomer.
 7. The hinged component of claim1, wherein: the live hinge includes a second layer of elastomer; and thetensile fabric is interposed between the first layer of elastomer andthe second layer of elastomer, each of the first and second layers ofelastomer being interposed between the tensile fabric and the materialsof the first and second portions of material where the live hinge isattached to each of the first and second portions.
 8. The hingedcomponent of claim 1, wherein the live hinge includes one end attachedto the first portion of material and an opposite end attached to thesecond portion of material, and at least one of the ends is at leastpartially embedded in the respective portion of material.
 9. The hingedcomponent of claim 1, wherein the live hinge includes one end attachedto the first portion of material and an opposite end attached to thesecond portion of material, and the first layer of elastomer extendsbetween the ends.
 10. The hinged component of claim 1, wherein the layerof tensile fabric and the first layer of elastomer are coextensive. 11.The hinged component of claim 8, wherein opposite ends of the live hingeare embedded in the respective first and second portions of material anda central portion of the live hinge is exposed.